Ultraviolet assisted pore sealing of porous low k dielectric films

ABSTRACT

Processes for sealing porous low k dielectric film generally comprises exposing the porous surface of the porous low k dielectric film to ultraviolet (UV) radiation at intensities, times, wavelengths and in an atmosphere effective to seal the porous dielectric surface by means of carbonization, oxidation, and/or film densification. The surface of the surface of the porous low k material is sealed to a depth less than or equal to about 20 nanometers, wherein the surface is substantially free of pores after the UV exposure.

BACKGROUND

The present disclosure generally relates to the manufacture ofsemiconductor devices, and more particularly, to an ultraviolet assistedpore sealing process for porous low k dielectric materials employed insemiconductor devices.

As semiconductor and other microelectronic devices progressivelydecrease in size, the demands placed on device components continue toincrease. For example, the prevention of capacitive crosstalk betweeninterconnect lines becomes significantly more important with smallerdevices. Capacitive crosstalk is generally a function of both thedistance between conductors and the dielectric constant (k) of thematerial placed in between the conductors. Considerable attention hasbeen focused on electrically isolating the conductors from each otherusing new insulators having low dielectric constants because althoughsilica (SiO₂), which has traditionally been used in such devices becauseof its relatively good electrical and mechanical properties, however asdevices scale to smaller dimensions dielectric constants below SiO₂'svalue of about 4 are required. These new low k (i.e., a dielectricconstant less than 4) materials are desirable for use, for example, asinter-layer dielectrics (ILD).

To achieve low dielectric constants, one can either use a material thatpossesses a low dielectric constant, and/or introduces porosity into thematerial, which effectively lowers the dielectric constant because thedielectric constant of air is nominally 1. Porosity has been introducedin low k materials through a variety of means. In the case of spin-onlow k dielectrics, a lowering of the k value can be achieved by usinghigh boiling point solvents, by using templates or by porogen basedmethods. However, the integration of porous low-k materials in themanufacture of the semiconductor device, in general, has provendifficult.

For example, because of the open nature of the porous low k dielectricmaterials, process gases and chemistries employed in subsequentprocessing (i.e., after formation of the porous low k dielectricmaterial)) may diffuse into the porous network where they become trappedwhere they can cause damage as well as alter the dielectric constant.Moreover, pores in direct communication with the surface can causepinholes to form in subsequent layers deposited and/or formed thereon,e.g., barrier layers.

Accordingly, there is a need in the art to provide improved methodstowards porous low k dielectric materials for integration intosemiconductor devices. Because of at least the problems noted with theprior art, it would be desirable to seal the porous low k dielectricprior to depositing additional layers and/or prior to furtherprocessing. Sealing the surface of the porous low k dielectric willadvantageously prevent penetration (and trapping) of process gases andchemistries. Moreover, sealing will provide a continuous surface layerfor coating/depositing additional layers thereon. Consequently, pinholeformation in subsequent layers can be substantially prevented.

BRIEF SUMMARY

Disclosed herein are processes for ultraviolet assisted pore sealing ofporous low k dielectric materials. In one embodiment, a process forsealing a porous low k dielectric material disposed on a substratecomprises exposing a surface of the porous low k dielectric material toan ultraviolet radiation pattern for a period of time, intensity andwavelength effective to seal the surface of the porous low k material toa depth less than or equal to about 20 nanometers, wherein the surfaceis substantially free of pores.

In another embodiment, a process for forming an electrical interconnectstructure comprises patterning a porous low k dielectric materialdisposed on a substrate; exposing the porous low k dielectric film toultraviolet radiation for a period of time, intensity and wavelengthpattern effective to seal the surface of the porous low k material to adepth less than or equal to about 20 nanometers, wherein the surface issubstantially free of pores; and depositing a barrier layer and/or aconductive layer onto the patterned porous low k dielectric material.

In another embodiment, a process for sealing a porous low k dielectricmaterial disposed on a substrate, comprises oxidizing a surface of theporous low k dielectric material by exposing the surface to anultraviolet radiation pattern for a period of time, intensity andwavelength effective in an atmosphere comprising oxygen to seal thesurface of the porous low k material to a depth less than or equal toabout 20 nanometers.

In yet another embodiment, a process for sealing a porous low kdielectric material disposed on a substrate comprises carbonizing asurface of the porous low k dielectric material by exposing the surfaceto an ultraviolet radiation pattern for a period of time, intensity andwavelength effective to seal the surface of the porous low k material toa depth less than or equal to about 20 nanometers.

In still another embodiment, a process for sealing a porous low kdielectric material disposed on a substrate comprises densifying asurface of the porous low k dielectric material by exposing the surfaceto an ultraviolet radiation pattern for a period of time, intensity andwavelength effective to seal the surface of the porous low k material toa depth less than or equal to about 20 nanometers.

In another embodiment, a process for sealing the pores of a dielectricmaterial deposited on a substrate comprising exposure of the substratewith ultra-violet radiation to alter the surface bonds to enable bondingsite for a subsequent material to be applied which would then seal thepores.

In another embodiment, a process for sealing the pores of a dielectricmaterial deposited on a substrate comprising exposure of the substratewith ultra-violet radiation in the presence of an oxidizing or reducingatmosphere to alter the surface bonds to enable bonding site for asubsequent material to be applied which would then seal the pores.

In yet another embodiment, a multi-step process for sealing the pores ofa dielectric material deposited on a substrate comprising exposure ofthe dielectric material with ultraviolet radiation with or without thepresence of an oxidizing or reducing atmosphere to alter the surfacebonds followed by the deposition of a sealing material which selectivelyreacts to the bonds formed by the UV process which then seals the pores.

In yet another embodiment, a multi-step process for sealing the pores ofa dielectric material deposited on a substrate, comprising exposure ofthe dielectric material with a sealant material or sealant precursor andthen exposing the substrate with ultra-violet radiation with or withoutthe presence of an oxidizing or reducing atmosphere to react the sealantwith the substrate and /or to alter the bonding structure of the sealingmaterial, which then seals the pores.

In yet another embodiment, a process for sealing the pores of adielectric material deposited on a substrate comprising the exposure ofthe dielectric material with a sealant material while exposing thesubstrate with ultra-violet radiation with or without the presence of anoxidizing or reducing atmosphere, where the ultra-violet radiationreacts with the sealant, with the substrate and /or both, which thenseals the pores.

The above described and other features are exemplified by the followingfigures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments andwherein like elements are numbered alike:

FIG. 1 graphically illustrates breakdown voltage as a function of pitchfor a circuit including a porous low k dielectric layer before and afterUV treatment in accordance with the present disclosure; and

FIG. 2 illustrates relative loss of porous dielectric material afterexposure to a hydrofluoric acid wet etching process as a function oftime, wherein some of the substrates with the porous dielectric materialdeposited thereon were exposed to UV radiation in accordance with thepresent disclosure in different environments.

DETAILED DESCRIPTION

The present disclosure is generally directed to a process for sealingporous low k dielectric films. The process generally comprises exposingthe porous surface of the porous low k dielectric film to ultraviolet(UV) radiation at intensities, times, wavelengths and in an atmosphereeffective to seal the porous dielectric surface by means ofcarbonization, oxidation, film densification, generation of surfacereactive sites that enable the chemical reaction of a deposited materialwhich then seals the pores, by deposition of a material that whensubsequently reacted with ultraviolet radiation seals the pores, and/orby deposition of a material that when concomitantly reacted withultraviolet radiation seals the pores. The UV assisted sealing processadvantageously provides a means for integrating porous low k dielectricmaterials within the integrated circuit manufacturing process.Optionally, after exposure to the ultraviolet radiation, furnaceannealing and like processes can be used to anneal the various depositedlayers as may be desired for some applications and manufacturingprocesses. As used herein, the term “porous low k dielectric materials”generally refers to those materials comprising a porous matrix whereinthe pore diameters are less than about 2 nanometers (nm) with aresultant dielectric constant (k) less than about 3.0.

The process for forming advanced electrical interconnect structuresgenerally comprises forming the porous low k dielectric material onto asubstrate and subsequently exposing the surface to an ultravioletradiation pattern for a time, wavelength, intensity and atmosphereeffective to seal the surface of the low k dielectric material or togenerate bonding sites for an applied sealing material. In oneembodiment, the ultraviolet radiation is effective to seal an exposedsurface of the porous low k dielectric material to a depth of 20nanometers, with a depth of about 10 nanometers more preferred, and adepth equivalent to an average pore diameter even more preferred.Although sealing the dielectric material can exceed 20 nanometers, it isgenerally less preferred for advanced semiconductor manufacturing sincesealing penetration impacts the bulk dielectric behavior of the low kmaterial. It has been found that sealing the porous low k dielectric toat least these depths substantially prevents subsequent damage to thedielectric material upon further processing. As such, process gases andchemistries employed during subsequent processing cannot penetrate theporous structure of the porous low k dielectric material. Moreover, bysealing the porous low k dielectric layer deposition and/or coating of asubsequent layer, e.g., a barrier or diffusion layer, can be made thatis substantially free of pinholes since the underlying porous dielectricmaterial includes a surface that is substantially pinhole free, i.e.,sealed. In the manufacture of integrated circuits, the diffusion orbarrier layer can be important as these layers can be used to form aboundary between the interlayer dielectric and the subsequentlydeposited conductive material such as copper metal interconnects, forexample.

Some examples of processes generally employed by those in the art thatmay be used to form the porous low k dielectric film include chemicalvapor deposition (CVD), plasma enhanced chemical vapor deposition(PECVD), high density PECVD, photon assisted CVD, plasma-photon assistedCVD, cryogenic CVD, chemical assisted vapor deposition, hot-filamentCVD, CVD of a liquid polymer precursor, deposition from supercriticalfluids, or transport polymerization (“TP”). Other processes that can beused to form the film include spin coating, dip coating,Langmuir-blodgett self-assembly, or misting deposition methods.

As used herein, the term “porous low k dielectric materials” generallyrefers to those materials comprising a matrix and a porogen, wherein thedielectric material after removal of the porogen has a porous structure.The term “porogen material” generally refers to those sacrificialorganic based materials known in the art that generate or form poreswithin the low k dielectric film after removal thereof. The porogenmaterials form domains (or discrete regions) in the matrix or matrixprecursor, which upon removal form pores in the matrix or matrixprecursor. Preferably, the domains should be no larger than the finaldesired pore size. In the present disclosure, suitable porogen materialsare not intended to be limiting and can include those materials thatdegrade upon exposure to thermal and/or photo radiation to form volatilefragments or radicals, which can be removed from the matrix material ormatrix precursor material under a flow of inert gas, for example. Inthis manner, upon exposure to the radiation, pores are formed within andthroughout the matrix, generally extending from a bottom surface to atop surface. As such, the resulting surfaces can comprise numerouspinholes.

Those porogen materials that are generally characterized in the art asthermally labile, thermally removable, photochemically labile,photochemically removable, and the like, are generally suitable forforming porous low k dielectrics. Materials of this kind are generallydescribed in U.S. Pat. No. 6,653,358, entitled, “A CompositionContaining a Cross-linkable Matrix Precursor and a Porogen and a PorousMatrix Prepared Therefrom”, the contents of which are incorporatedherein in their entirety by reference. Exemplary porogen materialsgenerally include, but are not limited to, hydrocarbon materials, labileorganic groups, solvents, decomposable polymers, surfactants,dendrimers, hyper-branched polymers, polyoxyalkylene compounds, orcombinations thereof.

Suitable matrices and matrix precursors generally include, but are notintended to be limited to silicon-containing polymers, or precursors tosuch polymers, e.g., silsesquioxanes such as alkyl (preferably loweralkyl, e.g., methyl silsesquioxanes, aryl (e.g., phenyl) or alkyl/arylsilsesquioxanes, and copolymers of silsesquioxanes (e.g., copolymers ofpolyimides and silsesquioxanes); adamantine based thermosettingcompositions; cross-linked polyphenylenes; polyaryl ethers;polystyrenes; crosslinked polyarylenes; polymethylmethacrylates;aromatic polycarbonates; aromatic polyimides; and the like.

For example, suitable silsesquioxanes are polymeric silicate materialsof the type (RSiO1.5)n, wherein R is an organic substituent.Combinations of two or more different silicon containing compounds canbe used. Other suitable silicon containing compounds for the porousdielectric material generally include materials including silicon,carbon, oxygen and hydrogen atoms, also commonly referred to as SiCOHdielectrics. Exemplary silicon containing compounds include (i) thesilsesquioxanes discussed above, (ii) alkoxy silanes, preferablypartially condensed alkoxysilanes (e.g., partially condensed bycontrolled hydrolysis of tetraethoxysilane having an Mn of about 500 to20,000), (iii) organically modified silicates having the compositionRSiO₃ and R₂SiO₂ wherein R is an organic substituent, and (iv)orthosilicates, preferably partially condensed orthosilicates having thecomposition Si(OR)₄.

Still further, silicon based dielectric precursors may includetetramethylcyclotetrasiloxane, hexamethylcyclotetrasiloxane,octamethylcyclotetrasiloxane, for example.

Another class of matrix precursors include thermosettablebenzocyclobutenes (BCBs) or b-staged products thereof. For example,1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethynyl)-1,1,3,3-tetramethyldisiloxane(referred to as DVS-bisBCB) is a suitable, the b-staged resin of whichis commercially available as CYCLOTENE® resin (from The Dow ChemicalCompany).

Another class of matrix materials include polyarylenes. Polyarylenes, asused herein, include compounds that have backbones made from repeatingarylene units and compounds that have arylene units together with otherlinking units in the backbone, e.g., oxygen in a polyarylene ether.Examples of commercially available polyarylene compositions includeSILK® dielectrics commercially available from The Dow Chemical Company,Flare® dielectric commercially available from Allied Signal, Inc., andVelox® which are poly(arylene ethers commercially available fromAirProducts/Shumacher). One class of polyarylene matrix precursors isthermosettable mixtures or b-staged products of a polycyclopentadienoneand a polyacetylene. Examples of the thermosetting compositions orcross-linkable polyarylenes that may be used in the composition includemonomers such as aromatic compounds substituted with ethynylic groupsortho to one another on the aromatic ring; cyclopentadienone functionalcompounds combined with aromatic acetylene compounds; and polyaryleneethers. More preferably, the thermosetting compositions comprise thepartially polymerized reaction products (i.e., b-staged oligomers) ofthe monomers mentioned above.

When the matrix precursor comprises a thermosettable mixture or b-stagedproduct of a polycyclopentadienone and a polyacetylene, the precursorsare generally characterized so that branching occurs relatively earlyduring the curing process. Formation of a branched matrix early on inthe cure process can minimize the modulus drop of the matrix, and alsocan help minimize possible pore collapse during the cure process.

Another example of a matrix precursor suitable for the preparation ofthe porous dielectric material is a thermosettable perfluoroethylenemonomer (having a functionality of 3 or more) or a b-staged productthereof, e.g., 1,1,1-tris(4-trifluorovinyloxyphenyl)ethane. Thethermosettable perfluoroethylene monomer may also be convenientlycopolymerized with a perfluoroethylene monomer having a functionality oftwo. Another suitable polyarylene matrix precursor is a thermosettablebis-o-diacetylene or b-staged product thereof.

Generally, the concentration of pores in the porous dielectric materialis sufficiently high to lower the dielectric constant of the matrix butsufficiently low to allow the matrix to withstand the process stepsrequired in the manufacture of the desired microelectronic device so asto maintain mechanical integrity (for example, an integrated circuit, amultichip module, or a flat panel display device). The density of poresis generally sufficient to lower the dielectric constant of the matrixto less than 3.0, in other embodiments, to less than 2.5 in otherembodiments, and to less than 2.0 in still other embodiments. In someembodiments, the concentration of the pores can be at least 5 volumepercent, in other embodiments, at least 10 volume percent, and in stillother embodiments at least 20 volume percent and generally not more than70 volume percent, and in yet other embodiments, not than 60 volumepercent based on the total volume of the porous matrix.

The average diameter of the pores within the matrix is generally lessthan about 20 nanometers (nm); with less than 2 nm in some embodiments;with not more than about 1 nm in still other embodiments.

During integrated circuit fabrication, the low k dielectric materialcontaining the porogen material is deposited onto a suitable substrateand exposed to a suitable energy source to remove the porogen and formthe porous low k dielectric structure. Suitable substrates include, butare not intended to be limited to, silicon, silicon-on-insulator,silicon germanium, silicon dioxide, glass, silicon nitride, ceramics,aluminum, copper, gallium arsenide, plastics, such as polycarbonate,circuit boards, such as FR-4 and polyimide, hybrid circuit substrates,such as aluminum nitride-alumina, and the like. Such substrates mayfurther include thin films deposited thereon, such films including, butnot intended to be limited to, metal nitrides, metal carbides, metalsilicides, metal oxides, and mixtures thereof. In a multilayerintegrated circuit device, an underlying layer of insulated, planarizedcircuit lines can also function as a substrate. However, the choice ofsubstrates and devices is limited only by the need for thermal andchemical stability of the substrate.

The UV assisted sealing process can employ a UV radiator tool, which, inone embodiment, can first be purged with nitrogen, helium, or argon toallow the UV radiation to enter the process chamber with minimalspectral absorption, especially for wavelengths less than about 200 nm,for example. The porous dielectric material is positioned within theprocess chamber, which is then purged separately with a desired processgas or gas mixture, such as N₂, H₂, Ar, He, Ne, H₂O vapor, NH₃, CO_(z),O₂, C_(x)H_(y), C_(x)F_(y), C_(x)H_(z)F_(y), and mixtures thereof,wherein x is an integer between 1 and 6, y is an integer between 4 and14, and z is an integer between 1 and 14, may be utilized for differentapplications. The particular process gas can be selected to selectivelypromote carbonization, and/or oxidation, and/or film densification bycrosslinking and/or formation of chemical reactive sites like Si—OH, forexample, during the UV exposure. In this regard, UV sealing can occurwithout the presence of oxygen, or with oxidizing gases, or withreducing gases, or with gases that specifically promote carbonization,or with gases that promote crosslinking, and like variations.

The UV assisted sealing process can employ a UV radiator tool, which, inone embodiment, can first be purged with nitrogen, helium, or argon toallow the UV radiation to enter the process chamber with minimalspectral absorption, especially for wavelengths less than about 200 nm,for example. The porous dielectric material is positioned within theprocess chamber, which is then exposed separately to ultravioletradiation and a desired sealant material, such as hexamethyldisilane(HMDS), trimethyldisilane (TMDS), diethylaminotrisilane (DEATS),trimethylchlorosilane (TCMS), etc., and mixtures thereof. The sealantmaterial may be introduced either before, during or after theultra-violet light exposure. In this regard, UV sealing can occurwithout the presence of oxygen, or with oxidizing gases, or withreducing gases, or with gases that specifically promote carbonization,or with gases that promote crosslinking, and like variations.

The UV light source can be microwave driven, arc discharge, dielectricbarrier discharge, or electron impact generated. Moreover, UV generatingbulbs with different spectral distributions may be selected depending onthe application.

The wafer temperature during the UV exposure may be controlled rangingfrom room temperature to 425° C., optionally by an infrared lightsource, an optical light source, a hot surface, or the light sourceitself. The process pressure can be less than, greater than, or equal toatmospheric pressure. Typically, the UV sealed porous dielectricmaterial is UV treated for no more than or about 450 seconds and, moreparticularly, between about 5 and about 300 seconds. Also, UV treatingcan be performed at a temperature of about room (ambient) temperature toabout 450° C., a process pressure that is less than, greater than, orabout equal to atmospheric pressure, a UV power between about 0.1 andabout 2,000 milliwatts per square centimeter (mW/cm²), and a UVwavelength spectrum between about 150 and about 400 nm. Optionally,sub-ambient temperatures can also be employed to minimize the extent ofsurface densification penetration to a depth of less than about 20 nm.

The extent of sealing can be measured by using standard analyticaltechniques. For example, transmission electron microscopy can beemployed as well as FTIR analysis. Also, because the surface propertiesof the low k dielectric change, changes in water contact angles can bemeasured to determine the extent of sealing. Still further, changes inwet etching rates and/or plasma etching rates can be monitored toprovide an indication of sealing effectiveness and penetration. In thismanner, throughput as well as the depth of sealing can be optimized fora particular application.

Advantageously, the UV curing process has been found to improvebreakdown voltage behavior and wet etch resistance while minimallyaffecting the bulk dielectric constant of the sealed porous dielectricmaterial. Moreover, FTIR analysis has shown that minor effects on filmsilanol content were observed for silicon based dielectric films.

In order that the disclosure may be more readily understood, referenceis made to the following examples, which are intended to illustrate theinvention, but not limit the scope thereof.

EXAMPLES Example 1

In this Example, breakdown voltage as a function of pitch was measuredbefore and after UV sealing the patterned porous dielectric material inaccordance with the present disclosure. Both substrates were annealed.The line width was 175 microns. As shown in the FIG. 1, a significantimprovement in the breakdown field was observed for the dense array.

Example 2

In this Example, substrates having deposited thereon a porous dielectricmaterial were exposed to a dilute hydrofluoric acid wet etching processfor different periods of time. The substrates were exposed to UVradiation in accordance with the present disclosure in an inertenvironment (purge-1), a reducing environment (purge-2), or an oxidizingenvironment (purge-3). A control was exposed to the wet etch processwithout any exposure to UV. The results are shown in FIG. 2, whichclearly show an increase in wet etch resistance upon exposure to the UVradiation as well as a dependence on the environment in which the UVexposure occurred.

While the disclosure has been described with reference to an exemplaryembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims.

1. A process for sealing an interlayer dielectric comprising a porouslow k dielectric material disposed on a substrate, the processcomprising: forming and patterning the interlayer dielectric comprisingthe porous low k dielectric material; exposing a surface of theinterlayer dielectric to an ultraviolet radiation pattern for a periodof time, intensity, and wavelength effective to generate surface bondsand form reactive sites on the surface prior to depositing additionallayers and/or prior to further processing; and reacting the reactivesites with a material to seal the surface, wherein the surface afterreacting the surface with the material is substantially free of openpores and a portion of the interlayer dielectric underlying the surfaceremains porous.
 2. The process of claim 1, wherein exposing the surfaceof the porous low k dielectric material to the ultraviolet radiationpattern for a period of time, intensity, and wavelength furthercomprises introducing a reactive gas during the exposure.
 3. The processof claim 2, wherein the reactive gas is composed Of N₂, H₂, H₂O vapor,NH₃, CO, CO₂, O₂, O₃, C_(x)H_(y), C_(x)H_(z)F_(y), and mixtures thereof,wherein x is an integer between 1 and 6, y is an integer between 4 and14, and z is an integer between 1 and
 14. 4. A process for sealing aporous low k dielectric material disposed on a substrate, comprising:forming and patterning an interlayer dielectric comprising the porouslow k dielectric material; exposing a surface of the interlayerdielectric to a sealant material and an ultraviolet radiation pattern ora period of time, intensity, and wavelength effective to generate asurface bonds and form reactive sites on the surface prior to depositingadditional layers and/or prior to further processing; and reacting thesealing material to seal the surface, wherein the surface issubstantially free of open pores and a portion of the interlayerdielectric underlying the surface remains porous.
 5. The process ofclaim 4, wherein exposing the surface of the porous low k dielectricmaterial to the ultraviolet radiation pattern for a period of time,intensity, and wavelength further comprises introducing a reactive gasduring the exposure.
 6. The process of claim 5, wherein the reactive gasis composed of N₂, H₂, H₂O vapor, NH₃, CO, CO₂, O₂, O₃, C_(x)H_(y),C_(x)F_(y), C_(x)H_(z)F_(y), and mixtures thereof, wherein x is aninteger between 1 and 6, y is an integer between 4 and 14, and z is aninteger between 1 and
 14. 7. A process for sealing a porous low kdielectric material disposed on a substrate, comprising: forming andpatterning an interlayer dielectric comprising the porous low kdielectric material; exposing a surface of the interlayer dielectric toa sealant precursor and ultraviolet radiation for a period of time,intensity, and wavelength effective to generate a surface bonds and formreactive sites on the surface prior to depositing additional layersand/or prior to further processing; and reacting the sealant precursorwith the reactive sites and surface bonds to seal the surface, whereinthe surface is substantially free of open pores and a portion of theinterlayer dielectric underlying the surface remains porous.
 8. Theprocess of claim 7, wherein a reactive gas is used during UV exposure toassist in the reaction with sealant material or sealant precursor. 9.The process of claim 8, wherein the reactive gas is composed of N₂, H₂,H₂O vapor, NH₃, CO, CO₂, O₂, O₃, C_(x)H_(y), C_(x)F_(y),C_(x)H_(z)F_(y), and mixtures thereof, wherein x is an integer between 1and 6, y is an integer between 4 and 14, and z is an integer between 1and 14.